1. Field of the Invention
The present invention relates to magnetic paint and objects coated the same, more particularly to magnetic paint comprising, as its essential components, a block copolymer and magnetic powder, the block copolymer having polyurethane and vinyl polymer segments, and objects coated the same.
The magnetic paint of the present invention exhibits outstanding effects as a magnetic recording medium for various purposes, including magnetic tapes, cards, prepaid cards and discs, and the objects coated with such magnetic paint can be used widely for the above purposes as a high-quality, magnetic recording medium.
2. Description of Related Art
Recently, demand has been increasing for audio tapes, home VTR tapes, magnetic tapes for computers, and floppy disks of higher quality, resulting from marked advances in hardware techniques for audio-visual devices, such as 8 mm videos, DATS, S-VHSs and high definition televisions, as well as computers, and the advent of higher-density recording media.
In particular, these recording media are required to be highly reliable during playback, and videotapes are required to reproduce high-quality images in addition to being highly reliable.
More concretely, they must have high-density recording ability in order to reproduce clear images and sound, to withstand high-speed movement for a long time under severe conditions, such as high temperature and high humidity, and to have sufficient adhesion between the magnetic layer and magnetic powder so that the latter will not come off from the former.
One of the important functions of the binder is to preserve these characteristics or properties of the magnetic layer. The binder is necessary to make the magnetic powder highly dispersable and to exhibit good electro magnetic characteristics, while maintaining high sensitivity, a high S/N ratio, a high CN ratio, and durability or resistant to wear and hydrothermal conditions.
A number of researchers have been developing various binders in an attempt to satisfy the above requirements. One of the major binders used to provide the magnetic layer with good wear-resistance and to improve the durability of the magnetic recording media is a blend of a vinyl chloride-vinyl acetate copolymer and a polyurethane resin.
However, several defects result depending on the extent of miscability between the vinyl chloride-vinyl acetate copolymer and the polyurethane resin. These defects include poor dispersability of the magnetic powder insufficient surface smoothness and low durability of the magnetic recording medium produced. At present, therefore, there are no binders with sufficient properties to achieve the above objectives, and objects coated with such magnetic paint are obviously unsatisfactory.